PURPOSE: To manufacture a magnetic thin film whose density is small and which is rich in flexibility by a method wherein a polymerizing monomer in an electrolytic solution is polymerized electrochemically on the surface of an electrode and magnetic-substance fine particles are contained in an electrolytically polymerized polymer.

CONSTITUTION: An action electrode and a counter electrode as well as a reference electrode as required are immersed in an electrolytic solution which contains a polymerizing monomer and a support electrolyte. Then, a voltage is applied and the polymerizing monomer is electrolytically oxidized or electrolytically reduced electrochemically. A reaction active species such as a cation radical, an anion radical or the like is generated in situ, it is polymerized, and a polymer is prepared. Then, magnetic fine particles are added to the electrolytic solution, the polymer is polymerized on the electrodes, and a magnetic thin film which contains the magnetic particles in the polymer obtained on a thin film is formed. Thereby, the magnetic thin film which is fine and whose shape is complicated can be obtained, and its film thickness can be controlled easily.